Apparatus for shaper cutting gears



May 18, 1954 W. 5. PRAEG APPARATUS FOR SHAPER CUTTING GE ARS Filed April 18, 1949 3 Sheets-Sheet 1 IN VEN TOR.

WALTER S. PRAEG BY 1/ 80 78 FIG.3.

ATTO EYs W. S. PRAEG APPARATUS FOR SHAPER CUTTING GEARS May 18, 1954 3 Sheets-Sheet 2 Filed April 18, 1949 wO h ll l l JNVENTOR.

WALTER S. PRAEG ATT NEYS Patented May 18, 1954 2,6 78,587 :hPPARKTU's Fo'R 's'HAPER CUTTiNGG'EhRS -Waiter 'S. 'Praeg, .Detroit fltlich assig'nor, by

t mesne assignments, to The -';Fe'llows Gear Sharer Company, Springfield, Vt, -a corporationmf Vermont niiiiimanain npnl 18, ISKQKSfidl Natalie 16 'Claims. i

ZDhe present ihVe'IffiiOh -fliitef's t?) allliijalf'atiis $61 shaper cutting gears.

According 130115116 present in'tiifitibil the gea r is shaperic'ut with a t'oothe'd teiil, the "Cutting pertiOll "Of which iS auspten 130 ih 156th 'tiiiebtions. :In =ornier to iirdv iiie-biittiiig eaLr-ance in back f Cutting 93213, the "-tee'th 5P6 6hgaged. in cutting are indi i-nec i Y htIy to the plane Of the gealr =du-ri n'g t'h diit't stroke, in

the di'irectihn which "will iire'iiuce ctitting ole'eir- I0 ance in b a'c'k 5f the eiitti g edge.

Conveniently, the r'ef'goin 'g is eiibbinpiished by providing a nutter ham a r i'gitl suppert poition, a :rigia 176691166 bifitih'g' pdffidh, "and a flexible web interconnecting the suppdrt pbi'tion and 1 the mutter po-r ti'on. 'Tiiis'toolin ybe -in the form of a rack or it "may be the "feiin of a circular cutter Such -as is 111 U. S. Paitht N0. $694,016 issued Jifly 2 291952. the latter-case the support Ipe'rtion 'com hub, the nutter iadi tion honfiiiise's a annular'rim havihg eu ttirig tseth thereen, and the Web comprises 21 reiati'veiy annular jiorti'dn adapted to fl'e'X iiii ri-l' igiipi eitioia 5f ithe 17001.

During operation and iniorer ti) previ'de for =a 25 definite invariable amouht er ineiina tien er the cutting teeth hum-1g their netting "passage, rigid ahutments :are provided seated at reueterminea distance at each side of the i ig id netting portion of the tool. 3

As a cutting tooth is inblined fiom its neutral position to cutting iposiiiion, theen'd o? the teeth which is lto effect the cutting oibera tibn mov'es outwardly of the toel toward the gear blank and the (opposite end of the te'dth moves inwardly of the tool away from the gear flel-ank. The position of the cutting edge during the cutting stroke is therefore spaced tower-tithe gear blank from its neutral position by a definite predetermined amount. Accordingly, finishing strokes erin making the iastfew strokes in finishing a. gean, -a situation may result in which the tooth of the cutter will not engage the material of the gear blank so as to be flexed to cutting position, even Tthb'iigh a email 'afnb'unt of excess material may remain hi1 the gear blejhk.

According to the present invention this di'ificulty is overcome "by prefleiiin'g the cutter so that the teeth which are to 'perfbim the mi g oper- 'atien are inclined te emper eutting position prior r in making very fine 40 to]. Tao-#8 merit *wi-ththe 'work smas to :p'rovi'de icuttingcle'arence in back =o'f the cutting edge.

"It is a fur ther ohject (if the present invention to provide mechanism operable automatically upcin initiation of a 'cutting stroke to he; the cutter fee as to incline the cutting teeth thereof inrior to engagement with the work.

It is "a further on; set lot the apresen't invention to Iprevide apparatus for "shaper cutting gears including a shaper :eu'tting tool bombrising a rigid sunpcirt portion, ia rigid cutting Spor'tion, "and a 'flexi'hie Web in'trco'nnetting these 'piortions, in conjunction with ir'iechanism tor preilexing the "cutting teethipi ior to engagement "with the work.

Other obje'ct's anti features of -the invention will becomezaupssrentlas thedescriizitiensbrobeeds, especially when taken in conjunction with the acc'dmpanying drawi-ngs, wherein:

Figure 1 is a vertical section through 2a machine "designed for employing a rack type flexible 'sh'aiper cutter.

Figure 2 is adiagrammatic view 'ofa cam structure employed therein.

Figure -3 "is an enlarged sectional view showing the tool flexing inechan'ism.

Figure '4 is an enlarged t'section on the line ii-'-"-'4,. Figi'1re 1.

Figure ="5 is a fragmentary side elevation partly iii-"sectionshowing inechanism'ior prefiexin'g a rotary flexible cutter.

Figure 6 :is a Zrear elevation fof the structure shown Figure '5.

Figure? is an enle-rgedsectional View through the flexible cutter and @refiexing mechanism.

Figure '8 (is at-side view of another embodiment of the present invention with parts insection.

Figure 911s airont elevation-of the tool mechanism shewn-in Figure 8. I

Figure '10 is a rear elevation of the .tool flexing structure. l

Figure is a siiie elevation 6f the structure shown in Figure 10.

F gure 12 is man View oi the structure "shown in Figure-1'11.

Figu e 13 is an enlarged "fragmentary view "iii-tanning the semen-between the toothed "cutter bar, the hearing fingers, and the rigid al utmems.

teetering new to Figure 1 th re s niusna tea a gear snaeer c prising s mam name 10 having ways l2 extending horizontally across the front bf the mabhi fie. Mounted for horizo'ntel teen anu forth traverse on these ways is a were table "M having -a feed hut 1 6 tamed thereby. The base of the frame 113 has mounted t5 thereon a teen shrew 1t empted to be rotated by suitable mechanism which is fragmentarily indicated by the table feed motor which is connected to the feed screw l8 by suitable gearing, one of the gears being indicated at 22. Mounted on the table I4 is a work supporting spindle adapted to mount a gear blank W at its upper end. At its lower end the spindle 2d carries a master gear 26 which may be identical with the series of gears to be finished by the machine. Rigidly carried by the frame to and meshing with the master gear 26 is a master rack 28. It will be apparent that traverse of the table M will result in predetermined rotation of the work spindle 24 and hence of the gear blank W.

While the master gear and rack may be identical as to the tooth formation with the gear to be cut and the cutting rack, it will normally be desirable to employ relatively fine pitch parts for controlling the rotation of the gear. In this way a more accurate control of the gear being out is obtained, since the number of teeth instantaneously in contact is increased. Moreover, this permits the use of a single master rack and a plurality of master gears, all of which are adapted to mesh with the single master rack.

A tool slide 30 is mounted on the upper portion of the base if} for adjustment toward and away from the work spindle 24, this direction of adjustment being from right to left as seen in Figure 1. gears of different, diameter as will be readily apparent. Mounted for vertical adjustment on the slide is a tool drive mechanism 3| which includes a crank 32 provided with a flywheel 3d and having a crank pin 36 secured thereto. The crank pin is radially adjustable on a plate 38 constituting a portion of the crank so as to provide for variation in stroke of the mechanism driven by the crank.

Located within the tool slide at is a motor 4d adapted to drive the crank in various positions of vertical adjustment through bevel gearing 32, change gearing 4 a worm it, and worm gear 38.

At the front of the drive mechanism 35 is a forwardly projecting portion 59 providing vertical guide way for a first tool flexing slide. 52.

A tool slide 54 is also mounted for vertical reciprocation and is guided by a channel member 56 bolted to, the tool flexing slide 52. The crank pin 36 is connected to a pin 58 carried at the upper end of the tool slide 5 3 by a connecting rod 62. At the inner end of the crank pin 36 is a cam surface 64 shown in detail in Figure 2. A connecting rod 66 is provided which connects the cam portion 6 5 of the crank pin to the tool flexing slide 52, and is provided at its upper end with a pair of opposed cam following rollers it.

The cutting tool T, as best illustrated in Figure 3, comprises a rigid cutting portion M having teeth 15, a rigid supporting bar it and a flexible web 78 interconnecting portions Hi and it. The support bar 16 is clamped at the lower end of the tool supporting slide 54 by a clamping strip 80 secured in place by a series of clamping screws 82. The forwardly extending portion 56 of the slide 52 has a downwardly and forwardly inclined flexing portion 84 adapted to engage the upper surface of the cutter bar 74. Secured to the lower portion of the slide 52 is a forwardly extending flexing plate 86 which is illustrated as fastened to the lower portion of the slide 52 by fastening screws 88. The extreme forward portion of the member 86 is shaped to provide an upwardly extending flexing portion 90 This adjustment is to accommodate 4 which engages the under side of the cutting bar 714.

The cam surface 64 is related to the eccentricity of the crank pin 36 such that upon initiation of a downward cutting stroke of the cutter slide 54, there is a relative upper motion of the cutter flexing slide 52. It will-be appreciated that this relative motion may in fact be accomplished by so designing the cam that the cutter slide 54 initiates its downward movement prior to the downward movement of the cutter flexing slide 52. The relative motion between the slides 52 and t l in the direction aforesaid will cause the cutter bar 74 to move upwardly with respect to the support bar it, accompanied by a flexing of the web J8 and this will incline the cutting teeth '15 in the proper direction for cutting on a downward stroke.

Upon completion of the downward cutting stroke and sometime prior to engagement of the cutter with the work gear W on the upper cutting stroke, there is a second relative motion between the slides 52 and 56 in the opposite direction which will have the effect of moving the cutting bar it downwardly with respect to the support bar it, thus inclining the cutting teeth 75 in the proper direction for cutting on the next stroke in the upward direction.

The flexing portions 64 and 9% of the cutter flexing slide may have slight clearance with respect to the upper and lower edges of the cutter bar "E4, or if preferred they may be in firm guiding engagement therewith and the contacting surfaces appropriately shaped to permit the flexing motion to take place.

Referring now to Figures 5, 6 and 7, there is illustrated a cutter and cutter support adapted to operate on a conventional gear shaper employing a circular gear shaper cutter. In this case the cutter spindle Hill is mounted for reciprocation in a direction transverse to the plane of the gear and preferably, in a direction parallel to the axis of the gear. In the actual apparatus employed the cutter spindle liltl' and the gear spindle will be geared together for rotation in timed relation as is well understood in the art. The flexible shaper cutter T comprises a rim lili having cutting teeth E82 thereon, the teeth being provided with cutting edges at both top and bottom ends. A rigid hub N33 is provided and a flexible web I94 interconnects the hub Hi3 and the rim Nil. Mounted at the lower end of the cutter spindle are a pair of rigid abutments H35 and Hit. The adjacent surfaces of the abutments are spaced apart a distance somewhat greater than the transverse width of the rim itl l, this dimension being indicated at IE3 in Figure '7. This dimension is selected so that when the rim lill is in engagement with the surface I09 of the lower abutment ltd, the cutting teeth I02 are inclined for cutting on the up stroke. Conversely, when the rim H3! is in contact with the lower surface lid of the upper abutment, the teeth 10: are properly inclined for cutting on the down stroke.

Loosely mounted on the abutment members I65 and H36 are a pair of rings H2 and H4 having reduced portions H5 and HS respectively for contacting with the upper and lower surfaces respectively of the rim ml.

Suitably mounted on a stationary part of the machine adjacent to the cutter support is a flexing device indicated generally at 12t. This device comprises a pair of levers I21 and I22 pivotally mounted to a supporting bracket 123 at pivots "l 24 and 1 25 respectively. Levers [2| 1 22 are interconnected by a link $26 so as to provide for parallel action of the-levers.

The lever -12! has an=erilarged=dircular friction portion 430 which received below a friction =p1ate f-31. Mounted on the pivot bdlt "I32 is a spring seat W33 and intermediate the spring seat 433 and the friction p'late |3I =are 1a plurality cf compression springs indicated at l'34. The "friction provided by this arrangement may "be varied in an obvious manner by tightening the nut I35.

The =forward end "of the levers 1 2i --and 422 have rounded contact portions l lfl-and W42 'respectively. Dhese portions are mairiteiined rat a constant spacing by the '-parallel :action resulting drom themse df ithe lirik I 26. fi vith the parts illustrated in the relation-of Figure 6, :the cutter is *moving in an upward -direction :and such in- "itial upward movement of the cutter spindle u'esuits in "establishment of pressure between the upper contact portion 4'40 of the lever i 21 and the upper ring H2. The upward motion oi the lever l2l was =0pp'osed by friction with the result that the rim portion r01 of the cutter was *moved downwardly :until it a'butted sthe upper surface 189 of the' lowerlabutment H16. IThereafter, movement :of :the cutter spindle 2| Ill? takes .place with the parts in the relation illustrated. Under (these circumstances ithe cutting .teeth Fl 92 are properly inclined for cutting :on the up stroke. itheinext vdown :stroke .is commenced the cutter spindle .moves 'rdownwardly establishiing pressure betweenithe il'owerring 3H5 and the ilower level .1522. BMotionzof thelever t22is op- :posed *byithe frictional imeans so that the cutter isareverselyxflexediand .the rim portion [01 engauges :the flower :surface :MB sof the upper .aLbutment A85. After zthenutterthas beenflexedifurther rmovement rof :the cutter is {of course =acnornplis'hed by corresponding .movement of the levers AMI :and M2 against theresistance iimclosed sbyithe frictionalrdevice.

While the .tltl ot ':the -.circular acutter and the bar "7.4 f the :rack xtype cutter :have rbeen defined :as relatively rigid, these Imenrhers .may he capable :of :some :fiexing. It :essential how- :ever that these members :have zsufficientirigidity lto :retain f the cutting teeth :in properly related .positiomso as 120 :flVOid. 'athe iintroductiion of errors :in the ".cut ggears. However, win the caserof the circular cutter it may. be lthat the :inclination ;of .the .cutting teeth in the scuttingazone may not extend for 2a wery :great distance beyond the cutting none, nor in other :words, the inclination :of :the teeth may result :from a more or :less' local bending -or :twisting ot the tooth supporting rim.

Since this is true it may be-desirable in some cases to provide the rings H 2 and IM relatively loosely "on the abutments 1'05 "and 1'06 so that when pressure applied through one of the "rings *to the rim 10!, the rings may incline so that "relative local twisting of the rim takes place.

Alternatively, it may "be ,possible to omit the rings 111.2 and I and .toso shape the flexing portions 140 .and 142 .of .the levers l2] and H22 respectively, that .they contact directly with the rupperandalowerzsuriaces respectively-of the cut ter vrim AM. in any :case, the flexing portions MB and 142 are locatedat the cutting zone.

Referring :now to Figures t8 rthmugh 13 there is. illustrated yet another zembodiment of the 6 present invention. In this case the machine comprises :a work spindle I 50 which is :mounted 'for rotation on a table (not -shown), the table being movable in ra direction perpendicular to the lane of the paper as seen in Figure 8. A master rack I 52 is :supported .on a stationary part of the machine frame as :by .an extension I54 bolted or otherwisesecured :thereto. .As indicated in Figure 58, the1master rack 152 may have an intermediate adjustable section P56 .in order to provide .for a controlled elimination of backlash. Rigidly secured on the workispindle 25B is a master 'gear I58 :adaptedtomesh with the master rack :and to produce .a controlled generating :rotation the work spindle as :it is abutment lit and detachably secured thereto is a second rigid abutment I12. .A rackztypeishaper cutter ['14 is provided and is :clamped to'the tool slide by the detachable abutment 112. The cutter li t comprises a :rigid -support abar Hi3 which is firmly iclamped in .the moolr-slide as illustrated, a toothed cutter *Iba-r 118,.anda flexible web interconnecting the supportibar alc'ifi Land the toothed cutterbar 1H8 soras toapermit flexing.

Means are provided iorfliexing the :cutter bar ilil prior to its engagement with a work piece W3, on a cutting stroke in either direction. This means takes the :form :of :a1flexingdeVice indicated generally at P82 and shown in detail in Figures 10, 11 and 112. The flexing device comprises an upper flexing member 184 )having a depending flexing finger 18.6, 22. lower flexing member I88 having an upper flexing 'finger lBEl. The flexing members .1184 and IBBzare connected together byside plates P92 and 19.4 which may be bolted or otherwisesecured thereto as indicated generally at I96. The members i8 1 "and 588 are each provided with openings 198 and 20s respectively for the reception :of a ,pin 2m seen in Figure 8. The pin 2.02 .has :an enlarged head portion294 which'is "cut away zto'provide a :fiat surface 2&6 for accommodating .a cam adjusting member 268. Thetintermediate portion 2 ill of the pin .is'reduce'd and .passes through the opening in the upperflexing member 1% and through a corresponding openingin :the forwardly projecting portion 'of the .tool slide 562. At its lower end the :pin 2.02 is irurther reduced :as indicated at? I 2, and passes ithrough the opening 208 provided in "the lower ifiexin'g :memcer i553. The parts are assembled'together with a clamping nut 2M illustrated in Figure 8.

The dimensions of the reduced intermediate portion 2H) of the pin :is such that :a predetermined amount oi clearance is provided between the lower surface of the .upper flexing imem'her I84 and the uppersurfacenf the (forwardly extending portion *ofuthe tool slidefand between the upper surface of therflexing member [83:and the lower surface of the forwardly projecting portion of the tool slide I762. The iflexing fingers I86 and 1 to extend longitudinally ofthermachine adjacent to the toothed bar 118 :of the cutter, and are adapted to engagethe same at awpointrspaced inwardlyifroin thercutting teeth provided thereon.

Means .are provided fiorrefiieeting ::a wertical adjustment between the tool slide 52 and the flexing device I82. The cam 208 is mounted on the tool slide [.62 for rocking movement about a pivot pin 220 and at its upper end it carries a cam engaging rolller 222. At its lower end the earn 208 has an inclined camming slot 224 in which is received a rollerg226 secured to the flattened side of the enlarged head 2% of the pin 262. As the cam 26% is rocked about the axis of the pin 229, the inclined camming slot 224 will effect appropriate vertical movement of the camming device I82 relative to the tool slide 52. In order to effect controlled rocking of the cam 208, there are provided a pair of fixed cam blocks 23E! and 232 in position to be engaged by the roller 222 as it approaches its lower or upper limit of reciprocation respectively. Cam blocks 236 and 232 are .rigidly secured to the stationary part of the frame 65% and are preferably adjustable thereon to accommodate different vertical strokes of the cutter slide.

With the parts in the position illustrated in Figure 9, which is an intermediate position, a downward stroke will cause the roller 222 to engage the cam block 236 and will rock the cam 203 in a clockwise direction. This will have the eifect of moving the flexing device I82 downwardly and will cause the flexing finger 35 to engage the upper surface of the toothed bar N8 of the rack and flex the same downwardly into engagement with the lower rigid abutment H2. This conditions the cutter for proper operation on the next cutting stroke, which is a cutting stroke in the upper direction. Flexing of the cutter to position the toothed bar H78 against the lower abutment [l2 rocks the toothed bar in a direction to provide the necessary cutting clearance in back of the cutting edges provided at the top ends of the rack teeth. The cam 298 will remain in the position to which it was moved by engagement with the cam block 23%]. Upon completion of the upper cutting stroke, the roller 222 will engage the other fixed cam block 232 and will rock the cam 268 in a counterclockwise direction. This will result in raising the flexing device H82 relative to the tool slide and will cause the lower flexing finger i9!) thereof to engage the toothed bar H8 and to move the same upwardly into engagement with the upper rigid abutment lid, thus conditioning the cutter for proper action on the next or downward cutting stroke.

In order to insure rocking motion of the toothed cutter bar H8 in the proper direction, the rigid abutments and the flexing fingers are designed in a particular manner to set up a torque on the cutter bar in the appropriate direction. This is illustrated in Figure 13 in which it will be observed that the rigid abutments my and H2 each are provided with inclined abutment surfaces 24d and 242 respectively. The top and bottom surfaces of the cutter bar I18 are inclined with respect to the abutment surfaces 240 and 242 and are adapted to engage therewith only by their corners 2M and 2% respectively. On the other hand, the flexing fingers $6 and lei! engage the cutter bar I18 at its forward edge directly adjacent to the roots of the cutting teeth. Accordingly, a flexing torque set up which tends to rotate the toothed bar l'lt in the proper direction. Thus for example, during the cutting stroke in the upper direction the flexing finger I86 will force the cutter bar H8 downwardly so that its corner 246 is in engagement with the inclined surface 242 of the lower abutment H2.

The fact that the flexing finger I84 is located outwardly beyond the point of engagement of the corner 24B and the surface 242, sets up a torque tending to rotate the cutter bar in a clockwise direction which is appropriate for a cutting stroke in the upper direction.

The teeth which are instantaneously engaged in cutting are thereby given a proper inclination for cutting and this inclination takes place in the proper direction in a plane passing through the axis of the cutter (in the case of the circular cutter), and also passing through the cutting zone between the cutter and gear. I

It will thus be apparent that mechanism is provided for initiating flexing a flexible gear shaper cutter so that it assumes proper cutting position prior to engagement with the work.

The drawings and the foregoing specification constitute a description of the improved method and apparatus for shaper cutting gears in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is: r

1. A rack type gear cutting machine comprising a cutting tool having a rigid support bar, a rigid toothed bar, and a flexible web intercon necting said bars, said toothed bar having teeth provided with cutting edges at the end thereof, a tool support comprising a reciprocating slide rigidly engaging said support bar, a flexing member movable with said slide in reciprocation and movable relative thereto, said member having means thereon engaging opposite sides of said toothed bar, and means operable upon initiation of each stroke of reciprocation to efiect relative movement between said slide and said member to flex said web to position the teeth of said toothed bar in clearance position.

2. A rack type gear cutting machine comprising a cutting tool having a rigid support bar, a rigid toothed bar, and a flexible web interconnecting said bars, said toothed bar having teeth provided with cutting edges at the end thereof, a tool support comprising a reciprocating slide rigidly engaging said support bar, a flexing member movable with said slide in reciprocation and movable relative thereto, said member having means thereon engaging opposite sides of said toothed bar, and cam means operable upon initiation of each stroke of reciprocation to effect relative movement between said slide and said member to flex said web to position the teeth of said toothed bar in clearance position.

3. A rack type gear cutting machine comprising a cutting tool having a rigid support bar, a rigid toothed bar, and a flexible web interconnecting said bars, said toothed bar having teeth provided with cutting edges at the end thereof, a tool support comprising a reciprocating slide rigidly engaging said support bar, a flexing member movable with said slide in reciprocation and movable relative thereto, said member having means thereon engaging opposite sides of said toothed bar, and a crank for reciprocating said slide and flexing member, independent connecting rods for connecting said crank to said slide and member, and cam means intermediate said crank and one of said connecting rods for effecting relative movement between said slide and member at the beginning of each reciprocation.

4. In a gear cutting machine, a reciprocating spindle, a cutting tool on said spindle comprising a rigid hub, a rigid toothed rim, and a flexible web intermediate said hub and rib, rigid annular abutments carried by said spindle and spaced slightlyyfrom theznormalrposition of said rim and. flexing members engageable with, said rim inwardly of the teeth thereon, and adjacent the, cuttingzone operable to flex; said rimLaga'inst one of said abutments upon initiation ofiarstrok of said spindle.

5. In a gear'cutting' machine; areciprocating spindlea cutting tool on: saim spindle comprising: a rigidihub, a rigid toothedmim, and a flexible web intermediate said hub and rib, rigid annular abutments carried by said spindle and. spaced slightly from the normal position of said rim and flexing members engageable with said rim adjacent the cutting zone operable to flex said rim against one of said abutments upon initiation of a stroke of said spindle, said flexing means comprising members movable with said cutter and brake means opposing such movement in both directions.

6. In a gear cutting machine, a reciprocating spindle, a cutting tool on said spindle comprising a rigid hub, a rigid toothed rim, and a flexible web intermediate said hub and rib, rigid annular abutments carried by said spindle and spaced slightly from the normal position of said rim and flexing members engageable with said rim adjacent the cutting zone operable to flex said rim against one of said abutments upon initiation of a stroke of said spindle, said flexing means comprisin parallel levers having end portions movable with said cutter and brake means opposing such movement in both directions.

7. In a gear shaping machine, a rack type gear cutter comprising a rigid support bar, a rigid toothed bar having teeth provided with cutting edges at both ends thereof, and a flexible web interconnecting said rigid bars; rigid abutment bars normally spaced transversely from said toothed bar, said abutment bars and toothed bar being shaped to abut at the edge of said toothed bar opposite to its teeth; and flexing fingers movable relative to said abutment bars to flex said toothed bar against one or the other of said abutment bars, said flexing fingers being shaped to engage said toothed bar at points spaced forwardly toward the toothed edge from the points of engagement of the abutment bars to set up a torque tending to rotate the toothed bar in the proper direction for the succeeding cutting stroke.

8. A gear shaper comprising a work support, a tool holder, means for effecting relative re ciprocation between said work support and tool holder, said tool holder being designed for use with a tool having a rigid support portion, a toothed cutting portion, and a flexible web interconnecting said support and cutting portions, said tool holder having means for rigidly gripping the support portion of said cutter, and a pair of members for gripping the toothed cutting portion of the tool inwardly of the teeth thereof and holding the cutting portion throughout the cutting stroke in position to flex the web of said tool and present the cutting teeth to the work with clearance in back of the cutting edges.

9. Apparatus as defined in claim 8 in which said members comprise a pair of rigid abutments mounted on said holder for movement relative to said means for gripping the support portion, and means operable before cutting during a cutting stroke to shift said members in a direction opposite to that of said stroke.

10. Apparatus as defined in claim. 3 in which one of said members comprises one of a pair of rigid abutments; fixed: on. said. holden at opposite sides: of: said: cutting portiong. and the otherw of saidimembersxcomprises Lone offa: pair ofs preflexe ing elements movable as. a unit on said holden and means operable before: cuttingsduringa each; cutting stroke to; shift; said elements in: an: op posite direction. to. position the cutting. portion" against oneaoff said: rigid: abutments.

11". Apparatus l as idefined in claim l'Oi comprising: an. actuator movable between", two i positions to'. effect; movement; of said: elements. and: cam: means operable" upon completion; ori' each: stroke for moving said actuator to position said elements properly for the next succeeding stroke.

12. Apparatus as defined in claim 11, said actuator comprising a pivoted lever, and a pin and slot connection between said lever and said elements, the inclination of the slot to the relative movement between the pin and slot making a small angle to insure against movement of said lever except when oamrned to one of its two positions.

13. A gear shaper machine comprising a work support, a tool holder, a tool comprising a rigid support portion, a toothed cutter portion, and a flexible web interconnecting said support and cutter portions, the teeth of said tool having cutting edges at both ends thereof, rigid abutments on said holder spaced at opposite sides of said toothed cutter portion shaped to engage said cutter portion inwardly of the teeth thereon to limit flexing thereof, and to provide a firm support for the cutting teeth closely adjacent thereto, preflexing means comprising a pair of elements spaced at opposite sides of said toothed cutter portion and engageable therewith inwardly of the teeth thereon, means for effecting relative reciprocation between said holder and said work support, and mechanism automatically operable in timed relation to each stroke of relative reciprocation to cause the element at the side of said toothed portion toward said work support to press said toothed cutting portion into engagement with the opposite rigid abutment prior to engagement with a work piece.

14. Apparatus as defined in claim 13 in which said preflexing means comprises a slide on said tool holder movable thereon in a direction perpendicular to the plane of the tool.

15. A gear shaper comprising a work support, a tool holder, means for effecting relative reciprocation between said work support and said tool holder, a cutter mounted in said tool holder, said cutter having an elongated base portion of substantial length rigidly fixed in said tool holder, an elongated tooth carrying rib portion spaced from said base portion, a multiplicity of spaced cutting teeth carried by said carrying rib portion, a flexible resilient web portion formed to extend substantially coextensively with said base and rib portions and joining said portions, and preflexing means engaging said tool inwardly of the teeth thereof and to hold the cutting portion throughout the cutting stroke in a position to flex the web of said tool and present the cutting teeth to the work with clearance in back of the cutting edges.

16. A gear shaper comprising a work support, a tool holder, means for eifecting relative reciproca tion between said work support and said tool holder, a cutter mounted in said tool holder, said cutter having an elongated base portion of substantial length rigidly fixed in said tool holder, an elongated tooth carrying rib portion spaced from said base portion, a multiplicity of spaced cutting teeth carried by said carrying rib por-' tion, a flexible resilient web portion formed to extend substantially coextensively with said base and rib portions and joining said portions, preflexing means engaging said tool inwardly of the teeth thereof and. to hold the cutting portion throughout the cutting stroke in a position to flex the Web of said tool and present the cutting teeth to the work with clearance in back of the cutting edges, and means operable in timed relation to the reciprocation between tool and work to actuate said preflexing means.

References Cited in the file of this patent 10 Number UNITED STATES PATENTS Name Date Eggers Oct. 22, 1912 Pigott Oct. 9, 1945 Laesser Dec. 2, 1947 FOREIGN PATENTS Country Date France Apr. 25, 1938 

